Tarnished (The Elder Tree Trilogy #1) by Erica Eberhart:
 
An outlawed magic, a hidden curse, and a love tested by fire.

In the struggling city of Braewick, a determined 20-year-old gate guard named Ailith MacCree longs for a chance at financial stability and adventure. Little does she know, her wish is about to come true. She accepts a mission from Princess Greer that promises both: escort Princess Caitriona to the Endless Mountains to meet the enigmatic hermit for a great financial reward. Ailith jumps at the opportunity and bids goodbye to all she’s ever known. But as they journey together, Ailith discovers that Caitriona holds a dangerous secret—she possesses powerful magic in a kingdom where magic is outlawed.

Ailith and Caitriona face mysterious attacks and supernatural challenges. But as they delve deeper into the treacherous landscape, Ailith learns of Caitriona's tragic past and the dark curse that threatens her very existence.

With rebellion brewing in Braewick, and the oppressive king hot on their trail, Ailith must not only navigate her growing feelings for Caitriona, but also fight against relentless foes. As they race against time to stop the curse, Ailith and Caitriona uncover shocking truths about their kingdom, their families, and themselves.

Will their burgeoning romance survive the trials ahead? Can they break the curse and save their homeland from tyranny? Join Ailith and Caitriona on a thrilling quest filled with magic, danger, and heart-pounding adventure. Fans of high-stakes fantasy will not want to miss this epic tale.